Strains of the species Lactobacillus delbrueckii subsp. bulgaricus are essential components of bacterial cultures used for the production of fermented milks and yoghurts in particular. Such strains usually produce lactic acid during the shelf life of the dairy products fermented with the bacterial cultures of which the strains are a component. This phenomenon is often referred to as “post—acidification”. Such strains do not usually contribute to the increased texture of the dairy products obtained by fermentation with the bacterial cultures of which the strains are a component.
According to the legislation in most EU countries, starter cultures to be used for the production of yoghurt must be composed of strains of the type Lactobacillus bulgaricus and strains of the type Streptococcus thermophilus. Furthermore, the acidification of milk takes place faster when starter cultures are composed of both types of strains, rather than one single type of strain alone.
A trend in the market for fermented milks is products with a moderate to a non-existent development of acidity during shelf life (low post-acidification) and a high texture (or viscosity). When selecting strains of the type Lactobacillus delbrueckii subsp. bulgaricus to be used either alone or as component of a culture for production of fermented milk and yoghurt, the product developer has to choose between the known strains that have the following combination of properties:                low post-acidification and low texturing power; or        high post-acidification and low texturing power; or        high post-acidification and high texturing power,as no Lactobacillus delbrueckii subsp. bulgaricus strains that in a satisfactory way combine a low post-acidification profile and a high texturing profile are available.        
Using any of the above known strains, the fermented milk product will either result in a high degree of post-acidification or a low texture, resulting from the use of the bacterial culture. The dairies often choose to work with cultures where the Lactobacillus delbrueckii subsp. bulgaricus strains combine low post-acidification and low texture. To increase texture in the fermented milk product, they add thickening agent(s) to the milk base before the fermentation takes place.